A decanter centrifuge of this kind is known from U.S. Pat. No. 5,354,255, which discloses a decanter centrifuge with a hollow bowl surrounding a rotating screw conveyor having a substantially cylindrical conveyor hub, which carries a screw comprising one or more flights. In order to resist the harsh environment encountered in many applications, the body as well as the screw of the screw conveyor of the type disclosed in U.S. Pat. No. 5,354,255 are typically manufactured in a resistant material such as steel.
A series of longitudinally extending and radially projecting supporting ribs is attached to the conveyor hub. Their cross-sectional area increases with the distance from the hub. Their purpose is to render possible reduction of the diameter of the conveyor hub, without detrimental impact on the capability of withstanding high speed operating conditions of thus formed structural unit comprising said hub and ribs. Such reduction of the hub diameter provides for reducing the diameter of the inner surface of a pond of supplied material in the separation chamber, which results in a reduced power demand of the decanter centrifuge.
However, the complex centrifuge design, as disclosed in U.S. Pat. No. 5,354,255, comprising radially projecting ribs renders its manufacturing rather difficult. In addition, ribs take up space in the bowl, thus reducing its useful volume.
WO-A-96/14935 discloses a very special decanter centrifuge mainly made of polyurethane. Thus WO-A-96/14935 discloses a decanter centrifuge having a drum and a conveyor with a hub and helical flights wherein the helical flights are made of polyurethane and are resting against the inner surface of the drum, which will stabilise the conveyor and provides a scraping effect on sedimented material. The material of the flights provides for a density of the flights in the same order as the density of the liquid phase of a material to be treated in the centrifuge, thus increasing the first critical vibration frequency of the conveyor, which provides for increasing the length or the rotational speed of the centrifuge thereby increasing its separation capacity. The hub of the conveyor is made of the same material as the flights i.e. the elastomeric material: polyurethane, whereby the conveyor is castable in a simple mould. To provide stiffness to the conveyor a pipe of carbon fibre reinforced resin is cast-in reaching from one end of the conveyor to the other between the bearings supporting the conveyor.